1. Field of the Invention
This invention relates to the preparation of polyurethanes including solid, non-cellular, and foamed urethanes, both rigid and flexible. In another aspect, the invention relates to a novel catalyst system for the preparation of polyurethanes which system exhibits a faster cure rate at ambient temperature than shown by either component of the catalyst combination when utilized separately.
2. Description of the Prior Art
Cellular polyurethane foams are usually prepared by the reaction between a compound containing at least 2 reactive hydrogen atoms as determined by the well-known Zerewitinoff method as described by Kohler in Journal of the American Chemical Society, 49,3181 (1927) and a polyisocyanate. In producing the foam, there are generally introduced various additives for blowing the polyurethane or emulsifying the urethane being formed and catalysts are utilized to promote the reaction within desirable time limits. Generally tertiary amine catalysts are used in combination with an organo-metallic compound such as stannous octoate or stannous oleate to promote the cross-linking reaction. In preparing such foams, the properties obtained are often dependent upon the water sensitivity in the typical polyisocyanate-polyol reactant mixture. The polyisocyanatewater reaction leads to the formation of carbon dioxide and thus more or less gas is generated depending on the presence of more or less water being present even in small amounts. It is also known to utilize as catalysts for the reaction certain mercuric salts of carboxylic acids, for instance, phenylmercuric acetate. These compounds as catalysts for the polyisocyanate-polyol reaction avoid to a substantial degree variations in foam properties as a result of the presence of moisture.
In the preparation of cross-linked, solid, non-cellular polyurethane polymers whether rigid or elastomeric, liquid mixtures of organic polyisocyanates and hydroxyterminated polyols have been reacted in the presence of certain mercury compounds as disclosed in U.S. Pat. No. 3,583,945 and U.S. Pat. No. 3,592,787, at ambient conditions of temperature without the use of heat or pressure. It is also known to catalyze the reaction of isocyanates with organic compounds utilizing metallic driers as catalysts in accordance with the teaching of U.S. Pat. No. 2,374,136. Thus cobalt naphthenate, manganese naphthenate, lead naphthenate and other metallic driers are known to catalyze the reaction. While other organo-metallic compounds such as stannous octoate or lead naphthenate are known to function as catalysts for the preparation of polyurethane foams, it is also known that zinc salts (carboxylates) are very poor catalysts for this reaction as disclosed in U.S. Pat. No. 3,347,804. Even combining 10% tin octoate with 90% zinc naphthenate provided a catalyst combination which showed an extremely slow foam rise time which was too slow to have commercial utility.
It is therefore particularly surprising that the applicants have discovered that the combination of an organo-mercuric compound with a zinc salt of an aliphatic carboxylic acid is an efficient co-catalyst which provides a means of accelerating the rate of cure at ambient temperatures for the reaction of an organic polyisocyanate and a compound containing at least 2 reactive hydrogen atoms, which catalyst combination is more effective than the use of the organo-mercuric compound when used alone as a catalyst.